Sams Teach Yourself MCSE Windows NT Server 4 in 14 Days
(Publisher: Macmillan Computer Publishing)
Author(s): David Schaer, et al
ISBN: 0672311283
Publication Date: 12/15/97

Installing the DHCP Server Service

To install the DHCP Server service on a Windows NT Server, do the following:

1.  Open the Control Panel/Network and select the Services tab.

2.  Choose the Add button.

3.  On the list presented, select Microsoft DHCP Server and choose OK.

4.  You will be asked for the path of the Windows NT Server 4.0 installation CD-ROM. Enter the drive letter of your CD-ROM drive or choose Browse to find the appropriate drive and the installation will then take place.

5.  Choose Close on the Network Control Panel.

6.  Verify that a static IP address, subnet mask, and default gateway have been assigned for each network adapter interface installed on the computer. After you have done this, choose OK and restart the computer.

After this is finished, the DHCP service should be running and will run automatically whenever the computer is started.

Creating a DHCP Scope

Before the DHCP server can assign IP addresses to client computers on the network, you must define a range of addresses it is allowed to assign. When you installed the DHCP server, the DHCP Manager software was also installed and is available from the Administrative Tools group within the Start menu. Use the following procedure to create a DHCP scope:

1.  Open the DHCP Manager and you should see a window similar to the one shown in Figure 11.5. The left pane of this window shows the server you are currently administering and the scopes that have been created on it (there should be none now). The right pane shows any options that have been defined for the current scope.

Figure 11.5.  The DHCP Manager main window.

2.  From the Scope menu, choose Create. The Create Scope dialog box shown in Figure 11.6 appears.

Figure 11.6.  Creating a scope with DHCP Manager.

3.  The Start Address and End Address fields define the range of the scope you are now creating. Enter valid IP addresses in these fields now.

4.  Enter a valid subnet mask in the Subnet Mask field.

5.  The Exclusion Range section of this window enables you to define one or more ranges of IP addresses within the current scope that you do not want the DHCP server to assign. You can define a range by entering the Start Address and End Address and choosing Add. You can exclude a single address by entering just the Start Address and choosing Add. You may remove excluded ranges by selecting the range and choosing Remove.

6.  You may also define the duration of the lease to be Unlimited or Limited To a specified amount of time.

If the number of available IP addresses and the number of DHCP clients are nearly equal, keep the duration of the lease short.

7.  You can add a name for your new scope and any comments you want to include. These are optional components and do not affect the scope in any way.

8.  When you are finished, choose OK and the Activate Scope Now dialog box appears, asking if you want to activate the scope. Choose Yes and you are returned to the DHCP Manager main window. Note that there will now be a scope defined for your server, denoted with a yellow light bulb icon, as shown in Figure 11.7.

Figure 11.7.  You have created your first scope.

If you want to modify the properties of this scope, you can do so by choosing Properties from the Scope menu of DHCP Manager. You can also activate, deactivate, and delete scopes using the appropriate choice under the Scope menu.

When you deactivate a scope, DHCP no longer can assign new leases to clients. It does not, however, cancel any leases that are currently active.

If you are configuring multiple DHCP servers on your network, Microsoft recommends that you split your pools of IP addresses. Each DHCP server should contain a scope with 75 percent of the IP addresses available on the local subnet. Each server should also have a scope containing the remaining 25 percent of available IP addresses for one other subnet.

Managing IP Address Leases

You can view and manage leases that have been assigned by DHCP by using the DHCP Manager. Under the Scope menu, select Leases and a window similar to the one in Figure 11.8 appears.

The information near the top of this window lets you determine the total number of leases available, how many are active or excluded, and how many are currently available. From this window you also can view the properties of or delete any individual active lease.

Figure 11.8.  Managing IP address leases using DHCP Manager.

Reserving IP Addresses Within a Scope

Although having DHCP assign IP addresses automatically is great, there are times when you must reserve IP addresses for specific DHCP clients. This enables that client to always be assigned the same address whenever it is initialized.

By reserving IP addresses on the DHCP server instead of simply configuring the client with a static IP address, the optional information that is passed along from a DHCP server to a client during initialization is preserved. This also allows more centralized management of addresses. To reserve a lease using DHCP Manager, use the following procedure:

1.  Select a scope for which you want to reserve a lease and choose Add Reservation under the Scope menu. This brings up the Add Reserved Clients window shown in Figure 11.9.

Figure 11.9.  Reserving a lease using DHCP Manager.

2.  In the IP Address field, enter the address you want that client to be assigned.

3.  In the Unique Identifier field, enter the MAC hardware address of that client. This can be determined by issuing the IPCONFIG /ALL command at a command prompt on a Windows NT client (refer to Figure 11.3). When you enter the MAC address, do not enter the dashes or any spaces.

4.  In the Client Name field, enter the name of the client computer.